This invention generally relates to boiler cleaning. More specifically, the invention relates to a retracting sootblower having a mechanism for articulating the sootblower and lance tube so that the lance tube can be inserted over multiple insertion axes through a single access port in a boiler.
Sootblowers are used to project a stream of blowing medium, such as water, air, or steam, against the heat transfer surfaces of the tube bank located within the boiler. The blowing medium is used to dislodge various combustion byproducts, including slag and ash, which becomes deposited on the heat transfer surfaces. If the encrustations are not removed, boiler efficiency significantly decreases. By using the blowing medium to dislodge the encrustation, the thermal and mechanical shock provided by the medium fractures the encrustations, breaking them free, and dislodges them from the heat transfer surfaces. Through effective and consistent sootblowing, the efficiency of the boiler can be maintained.
The present invention pertains to sootblowers of the type or category which are retractable. A retractable sootblower is located outside of the boiler and its lance tube is periodically advanced into and withdrawn from the boiler to perform cleaning. One or more nozzles are located on the end of the lance tube and project jets of the blowing medium. While being inserted and retracted, the lance tube is rotated so that the jets trace helical paths across the heat transfer surfaces.
The present invention pertains to the modification of a retractable sootblower of the type illustrated in U.S. Pat. No. 5,605,117 which is articulable so that the lance tube can be inserted into and retracted from a boiler over multiple insertion axes, but through a single or common access port. The sootblower includes an exteriorly located frame mounted adjacent to a wall box or access port in the boiler wall. A carriage assembly is supported by the frame and coupled to a lance tube which has at least one nozzle at its distal end. The lance tube generally defines the axes along which it will be inserted into and withdrawn from the interior of the boiler. As the lance is inserted, retracted or both, it is also rotated by the carriage assembly through a mechanical translational drive.
An advantage of this type of single motor rack and pinion driven sootblower is that it is economical to manufacture. The single motor is used not only for translational drive of the carriage assembly, but also used to rotationally drive the lance tube through the mechanical translational gear drive. This single motor is generally driven through the use of a programmable controller.
However, a disadvantage of such a single motor rack and pinion driven sootblower is that the mechanical translational drive provides fixed indexing of the rotational drive for the lance tube and the lance tube rotation is a function of the traversing speed. Accordingly, as is taught, for example, in the disclosure of U.S. Pat. No. 5,579,726, it is preferable that such retractable rack and pinion driven sootblowers have separate independent motors for transverse drive of the carriage assembly and rotational drive of the lance tube. This permits independent driving of the two motors through the use of a microprocessor which permits infinite indexing for both reverse helix cleaning and cross helix cleaning and the ability to switch the pitch during sootblower operation and to change the oscillating mode.
Accordingly, it is a principal object of the present invention to provide a method and apparatus for converting a retractable single motor driven sootblower of the type disclosed in U.S. Pat. No. 5,605,117 to a dual motor drive for independently controlling the traversing motor and the rotary motor for thus enhancing the cleaning ability of the sootblower by allowing the motion of the lance tube to be infinitely changed or varied.